LASER HAZARD TRAINING GUIDE
1.0
LASER FUNDAMENTALS
The term "laser" is an acronym for "Light Amplification by Stimulated Emission
of Radiation." A laser is a device that utilizes the natural oscillations of atoms
or molecules between energy levels for generating electromagnetic radiation
which is coherent, parallel beam, and monochromatic. The laser consists of
three basic components: (a) the lasing medium - which can be solid, liquid
(dye), gas, or semiconductor; (b) the optical cavity - which contains the
medium to be excited between mirrors which redirect the produced photons
back along the same parallel path; and (c) the pumping system - which uses
photons from another source to transfer energy to the medium.
Figure 1 Laser Components
2.1
TYPES AND CHARACTERISTICS OF LASERS
Lasers can be classified by a number of physical and operational
characteristics including the lasing medium, wavelength, temporal mode of
operation, and beam power (see Tables 1 and 2 in the Appendix B).
2.2
Lasing Medium
The lasing medium is the characteristic most often used to designate the laser
type. Carbon dioxide, helium-neon, xenon, dyes, ruby, and neodymium-YAG
are examples of materials widely used as lasing mediums. The particular
material selected as the lasing medium will, in turn, determine the laser's
wavelength.
1
2.2
Wavelength
The absorption and transmission characteristics of a given laser are
determined largely by its wavelength. Laser wavelengths typically range from
10-3 to 103 micrometers with this range being divided into three general regions:
(1) ultraviolet; (2) ocular focus; or (3) infrared. The ocular focus region, which
contains the visible portion of the spectrum, extends from 0.4 to 1.4
micrometers.
Figure 2 Laser Spectral Region
2.3
Temporal Mode of Operation
Lasers are also classified by the rate at which they emit radiation over time. In
general, laser radiation is emitted in one of two time modes: (1) continuous
wave; or (2) pulsed. Continuous wave lasers produce a steady stream of
photons with a beam power which remains constant over time. Pulsed lasers
emit "bursts" or pulses of photons with each pulse being less than 0.25
seconds in length. The pulse duration of most pulsed lasers ranges from
milliseconds to picoseconds.
2.4
Beam Power
One of the most important characteristics of the laser in determining its hazard
potential is beam power or energy. For continuous wave lasers, the beam is
characterized by its power density (or Irradiance) in watts/cm2, which is a
function of beam diameter and the laser's output power. Pulsed lasers are
characterized by their energy density (or Radiant Exposure) in joules/cm2,
which is dependent upon the beam diameter and the energy of an individual
pulse.
2
3.0
LASER REFLECTIONS
Laser beams are reflected to some extent from any surface contacted. If the
reflected rays remain parallel (i.e., the angle of reflection equals the angle of
incidence), the reflection is called "specular". If the reflected rays are randomly
scattered, the reflection is called "diffuse". Specular reflections are produced
by highly polished, mirror-like surfaces whereas diffuse reflections result from
rough, irregular surfaces (however, specular reflections can also be produced
by rough surfaces when the size of the surface irregularities is less than the
wavelength of the incident radiation). The distinction between a specular
reflection and a diffuse reflection is not always clearly defined. Except for
reflections from precisely constructed optical mirrors, all beams are to some
extent divergent. In general, however, the rougher the reflecting surface, the
greater will be the divergence (or diffuseness) of the reflected beam and the
less will be its corresponding hazard potential.
Figure 3 Types of Laser Reflections
4.0
LASER HAZARDS
The hazards that are associated with the use of lasers can be divided broadly
into (1) those present from the "direct" effects of the laser beam upon human
tissue; and (2) those posed "indirectly" by the laser beam or by the physical,
mechanical, chemical, or electrical aspects of the laser system.
3
4.1
Biological Effects of Laser Radiation
Laser radiation can damage living tissue by two basic mechanisms. For
continuous wave lasers, the mechanism is a thermal process whereby a
steady stream of photons is absorbed by the tissue until the natural cooling
ability of the tissue is overwhelmed and its temperature rises to damaging
levels. For pulsed lasers, the mechanism is one of blast or shock damage as
individual pulses vaporize water within cells. In general, this second
mechanism tends to be more important in inflicting serious permanent damage
to tissue. A third mechanism (termed photochemical damage) is important
only for ultraviolet lasers and can produce cataracts and skin cancer from
which long term exposures.
4.1.1
Eye Damage
By far the most important site of damage from laser radiation is the eye. The
location and extent of the damage inflicted is dependent upon the wavelength
of the radiation and the energy of the beam (or its individual pulses).
Radiation with wavelengths in the ocular focus region (0.4 - 1.4 micrometers) is
transmitted through the cornea and focused by the lens on the retina with a
magnification of up to 100,000 times. Laser beams with wavelengths in this
range have the greatest potential for seriously damaging the eye by virtue of
their ability to form permanent lesions on the retina.
Figure 4 Absorption and Transmission of Laser Light by
Components of the Ocular System
4
Laser radiation with wavelengths outside the ocular focus region are largely
absorbed by the cornea and thus do not pose a hazard to the retina. In the
infrared (1.4 -1000 micrometer wavelength), excessive exposure causes a loss
of transparency or surface irregularities in the cornea. In the ultraviolet (0.2 to
0.4 micrometer wavelength), excessive exposure produces photophobia
(intolerance to light) accompanied by redness, tearing, conjunctival discharge,
surface exfoliation (removal of the surface in scales or laminae), and stromal
haze (cloudiness in the connective tissue or main body of the cornea).
4.1.2
Skin Damage
The skin's large surface area makes it readily available to accidental and
repeated exposures to laser radiation. In the visible and infrared regions, the
biological significance of skin irradiation is considerably less than that for the
eye since skin damage is usually repairable. Effects vary from mild erythema
(reddening) to blisters or charring. Depigmentation, ulceration, and scarring of
the skin as well as damage to underlying organs can occur from extremely
high-powered laser radiation. Though little data exists on the effects of skin
exposure to ultraviolet laser radiation, the ability of the ultraviolet portion of
solar radiation to produce various grades of erythema, skin aging, and cancer
is well known.
4.2
Other Laser Hazards
The potential health and safety hazards associated with laser systems are not
limited to the effects of the beam upon the eye or skin from direct or specularly
reflected beams. A number of other physical, chemical, or electrical hazards
may be posed from the operation of these systems.
4.2.1
Airborne Contaminants
Many of the materials required for laser operation as well as materials
produced by the laser during operation (as by beam interaction with target
materials) are potentially hazardous to operating personnel. Laser media,
fuels, or exhaust products can include carbon monoxide, carbon dioxide,
nitrogen oxides, sulfur dioxide, sulfur hexafluoride, nitrogen, helium, hydrogen,
fluorene, hydroflouric acid, and various refrigerants. Beam interaction with the
target can produce a "plume" which, depending upon the nature and
composition of the target, can include metallic fumes and dusts, chemical
fumes, organic solvents, polycyclic aromatic compounds, hydrogen cyanide, or
biological contaminants. All of these materials pose potential inhalation
hazards to those working with or near the laser system.
4.2.2
Explosions
Laser targets, bulbs, and high-pressure filaments and lamps may shatter
during operation propelling projectiles throughout the vicinity of the laser. For
this reason, adequate enclosure of these components is essential.
5
4.2.3
Fire Hazards
Solvents used in dye lasers are extremely flammable and have led to
numerous fires in laboratories throughout the United States. Many of these
fires were started by a high-voltage pulse through an alcohol solvent. Highpower continuous wave infrared lasers can also pose substantial fire hazards.
The direct and specularly reflected beams of these lasers can ignite flammable
materials in the area of laser operation.
4.2.4
Electrical Hazards
The high-energy electrical power supplies of many laser systems pose a
serious hazard of electrical shock or electrocution. In fact, electrocution is the
major cause of death from accidents involving lasers.
4.2.5
Cryogenic Hazards
Liquid nitrogen and other cryogenic fluids are utilized in cooling some lasers
and photodetectors. Upon evaporation, such cryogens can pose an
asphyxiation hazard by displacing breathable oxygen. Cryogenic fluids are
also potentially explosive if stored improperly or used in inappropriate
containers or plumbing.
5.1
LASER SAFETY
The American National Standard for the Safe Use of Lasers (ANSI Z136.12014) serves as the fundamental guide to laser safety in the United States.
This standard describes criteria for evaluating the overall hazard potential of a
laser system, a laser classification scheme which is based upon hazard
potential, and specific control measures for minimizing laser hazards.
5.2
Laser Hazard Evaluation
ANSI Z136.1 states that an evaluation of the total hazard potential of a
particular laser must take into consideration three primary factors:
1. The laser's capability of injuring personnel.
2. The environment in which the laser is used.
3. The personnel who may use or be exposed to the laser's radiation.
Item 1 has been addressed by the ANSI standard through its establishment of
a classification scheme for lasers by hazard potential. This classification
scheme includes a range of recommended control measures for the various
hazard classes. Items 2 and 3 vary with each laser application and thus are
not readily addressed by a classification system. They will, however,
determine the extent to which the controls suggested for the particular hazard
class are needed.
6
5.2
Laser Hazard Class
ANSI Z136.1 establishes four general hazard classes based upon the ability of
the primary laser beam and its specular reflections to cause biological damage
to the eye or skin during the intended use. The specific criteria, in terms of
beam characteristics and accessible emission limit (AEL), for designation
within each class are found within the ANSI standard (see Tables 1 and 2 in
the Appendix to this guide). In general, the characteristics of lasers within
each hazard class are as follows:
Class 1 Low-power lasers, which pose no risk to the skin or eyes.
Class 2 Low-power lasers that pose no risk to the skin and minimal risk to the
eyes (i.e., the aversion response of the eye will normally afford
sufficient protection).
Class 3 Medium-power lasers whose direct beam and specular reflections
pose no risk to the skin and minimal risk to the eyes (Class 3R) and
medium-power lasers whose direct beam and specular reflections
pose potential risks to the skin and immediate risks to the eyes
(Class 3B)
Class 4 High-power lasers whose primary beam and reflections (both
specular and diffuse) pose immediate risks to the skin and eyes.
5.3
Laser Terms





Accessible exposure limit (AEL) - The maximum allowed power within a
given laser classification.
American National Standards Institute (ANSI) - The technical body which
releases the Z136.1 Standard for the Safe Use of Lasers.
Average power - The average power of a pulsed laser is the product of the
energy per pulse (J/pulse) and the pulse repetition frequency (Hz or
pulses/sec). The average power is expressed in Watts (J/sec).
Coherent radiation - Radiation whose waves are in-phase. Laser radiation is
coherent and therefore very intense.
Continuous wave (CW) - A term describing a laser that produces a
continuous laser beam while it is operating (verses a pulsed laser beam).

Diffuse reflection - When an incident radiation beam is scattered in many
directions, reducing its intensity. A diffusely reflecting surface will have
irregularities larger than the wavelength of the incident radiation beam. See
specular reflection.
7











Health Care Laser System (HCLS) - Laser systems used in health care
applications, and includes a delivery system to direct the output of the laser, a
power supply with control and calibration functions, mechanical housing with
interlocks, and associated fluids and gases required for the operation of the
laser.
Intrabeam exposure - Exposure involving direct on-axis viewing of the laser
beam. Looking into the laser beam would constitute intrabeam exposure.
NOTE: Intrabeam viewing of lasers is not permitted on campus.
Infrared (IR) radiation - Invisible radiation with a wavelength between 780 nm
and 1 mm. The near infrared (IR-A) is the 780 to 1400 nm band, the mid
infrared (IR-B) is the 1400 to 3000 nm band, and the far infrared (IR-C) is the
3000 nm to 1 mm band
Irradiance - The power being delivered over the area of the laser beam. Also
called power density, irradiance applies to CW lasers and is expressed in
W/cm2.
Laser - Light Amplification by Stimulated Emission of Radiation. A
monochromatic, coherent beam of radiation not normally believed to exist in
nature.
Laser Controlled Area - An area where the occupancy and activity of those
within is subject to control and supervision for the purpose of protection from
radiation hazards.
Laser User - Any person who uses a laser for any purpose on the IUPUI
campus.
Laser Safety Manual - A document defining the IUPUI Laser Safety Program.
Laser Use Registration (LUR) - The mechanism used by the Office of
Environmental Health and Safety to track lasers on campus. The LUR details
the safety requirements for each Class 3b and 4 laser.
Laser Safety Officer (LSO) - A member of the EHS staff, the LSO is
responsible for implementation of the Laser Safety Program.
Maximum Permissible Exposure (MPE) - The maximum level of radiation
which human tissue may be exposed to without harmful effect. MPE values
may be found in the IDNS Standard.
Material Safety Data Sheet (MSDS) - A document, required by law, which is
supplied by the manufacturer of a chemical. The MSDS details the hazards
and protective practices required for protection from those hazards, as well as
other information.
8










Nominal Hazard Zone (NHZ) - The area surrounding an operating laser where
access to direct, scattered or reflected radiation exceeds the MPE.
Optical Density (OD) - Also called transmission density, the optical density is
the base ten logarithm of the reciprocal of the transmittance (an OD of 2 = 1%
transmittance).
Peak power - The highest instantaneous power level in a pulse. The peak
power is a function of the pulse duration. The shorter the pulse, the greater the
peak power.
Plume - Aerosol created by vaporization of tissue or metals that may contain
viable bacteria, virus, cellular debris, or noxious and possibly toxic metallic
fumes.
Physician/Principal investigator (P/PI) - The person directly responsible for
the laser and its use. The CP/PI has direct responsibility for all aspects of
safety associated with the operation of laser systems in either the clinical or
laboratory environment.
Radiant exposure - The energy being delivered over the area of the laser
beam. Also called energy density, radiant exposure applies to pulsed lasers
and is expressed in J/cm2.
Specular reflection - Results when an incident radiation beam is reflected off
a surface whose irregularities are smaller than the radiation wavelength.
Specular reflections generally retain most of the power present in the incident
beam. Exposure to specular reflections of laser beams is similar to intrabeam
exposure. See diffuse reflection and intrabeam exposure.
Standard Operating Procedures (SOP) - A procedure that explains operating
and safety practices specific to a laser or laser system.
Ultraviolet (UV) radiation - Invisible radiation with a wavelength between 10
nm and 400 nm. The near ultraviolet (UV-A) is the 315 to 400 nm band, the mid
ultraviolet (UV-B) is the 280 to 315 nm band, the far ultraviolet (UV-C) is the
100 nm to 280 nm band, and the extreme ultraviolet is the 10 to 100 nm band.
Visible Light - Radiation that can be detected by the human eye. These
wavelengths are between 400 and 780 nm. The colors (with approximate
wavelengths) are: Violet (400 - 440 nm), Blue(440 - 495 nm), Green (495 - 545
nm), Yellow (545 - 575 nm), Orange (575 - 605 nm), and Red (605 -780 nm).
9
REFERENCES
American National Standard for the Safe Use of Lasers (ANSI Z136.1 2014), The Laser Institute of America, Orlando, Florida, 1993.
A Guide for Control Of Laser Hazards, American Conference of
Governmental Industrial Hygienists, Cincinnati, Ohio, 1990.
Fundamentals of Industrial Hygiene, National Safety Council, Chicago,
Illinois, 1988.
Introduction to Health Physics, H. Cember, Pergamon Press, 1985.
Safety with Lasers and Other Optical Sources, D. Sliney and M. Wolbarst,
Plenum Press, 1981.
10